"Copyright © 2015 by ASWATH. Published by The Mars Society with permission"

Abstract— The paper describes various issues faced by rover in

an alien environment and attempts to solve each of them using

innovative design modifications. The rover features a bio-

inspired eight-wheeled drive mechanism, an integrated robotic

arm and a stereo vision technique for advanced image

processing. The system control, for both the rover as well the

robotic arm, is done using microcontrollers and microprocessors

such as Arduino, Intel NUC, and Raspberry Pi. Inspired from

nature, a reflex mechanism has also been integrated into the

rover design to minimize damage, by automated safety reflexes.

The arm is so designed to switch between three different end

effectors depending upon the task to be performed. The 8-

wheeled rover combines the rocker bogie mechanism and four

rocker wheels and four spider-leg wheels. The spider-legs

ensures that it can traverse over a considerable height greater

than the chassis height which could be as much as thrice the

diameter of the wheels ,whereas the current NASA`S curiosity

rocker bogie system can only traverse over a height twice the

diameter of the wheel. Additionally, as they are actuator-

powered, the slope of the rover can be adjusted in such a way that

it does not topple for a wide range of inclination and allows the

rover to traverse over highly rugged terrain. It provides a large

amount of traction with the ground even in terrains where there

is a negative slope or vertical drop of around 1m using a spring-

damper suspension mechanism whereas the rocker bogie

mechanism provides traction only due to its body weight The

Rover finds applications in the exploration of other planets, deep

sea vents and other hostile environments. It offers a possibility of

integrating numerous features such mineral collection and

sampling, landscape mapping, moisture detection etc. Such an

effort may even prove to be instrumental in detection and study

of biological activity in worlds other than ours.

I. INTRODUCTION

The Mars Rover is a vehicle that has been designed to traverse

the rugged terrains of Mars and collect samples of various

items on Mar’s surface. Scientists over the years have tried to

explore the possibility of life on Mars. Such explorations have

been mostly done using rovers. Hence rovers need to be

specially designed to traverse all kinds of terrains and must be

equipped with state of the art technology. A common design

element is most rovers over the years is the rocker bogie

mechanism. The rocker bogie mechanism has quite a lot of

advantages and is hence a well-established mechanism. The

main advantage is that it ensures that all the wheels of the

Aswath S, Deepu P Mathew, Chinmaya Krishna Tilak, Amal Suresh, Ragesh

Ramachandran, Arjun B Krishnan and Unnikrishnan VJ is with Electronics and

Communication Department, Amrita Vishwa Vidyapeetham, Kollam, Kerala 690525

INDIA (corresponding author to provide phone: +919995766565;

e-mail: aswathashh10@gmail.com, and balasreeunnikrishnan@gmail.com).

rover are in contact with the ground at all times. This

advantage is key to creating a stable all terrain system.

Consequently the traction of the rocker bogie provides is equal

and reliable allowing a smooth running even on the uneven

terrains.

The earliest notable Mars explorer, the Pathfinder, landed on

Mars with a fully function rover on Mars on July 4, 1997.The

rover carried a wide array of scientific instruments to analyze

the Martian atmosphere, climate, geology and its rock and soil

composition. Sojourner, the Pathfinder’s rover, made

observations that answered numerous questions about the

origin of the rocks and other deposits on Mars. Following its

stead, the Opportunity successfully investigated soil and rock

samples and managed to take panoramic images of its landing

site giving us valuable information about the Martian terrain

and other site conditions. It is the data that was collected in

these missions, using sampling technology, which allowed

scientists at NASA to theorize about the presence of

hematite and consider exploring the possibility of finding

water on the surface of Mars. Curiosity, another historic

milestone in the history of alien planet exploration, was

assigned the role of investigating

Martian climate and geology. It assessed whether the selected

field site, Gale Crater, had ever offered environmental

conditions favorable for microbial life and future investigated

the role of water in planetary habitability as preparation for

future human exploration [1-4]. In these types of rover’s only

6-wheeled rocker bogie [5-12] suspension is used.

This paper proposes an 8-wheeled rover which combines four

rocker wheels which form the rocker bogie mechanism along

with four spider-leg wheels. The figure.1 shows the Solid

Works model of the rover. The spider-legs ensures that it can

traverse terrains with heights much greater than the chassis

height. Additionally, since the wheels are actuator-powered,

the slope of the rover can be adjusted in such a way that it does

not topple for a wide range of inclination and allows the rover

to traverse over highly rugged and uneven terrain, It provides

a significant amount of supplemented traction with the ground

even in terrains where there is a negative slope or vertical drop

of around 1m using a spring-damper suspension mechanism.

Sreekuttan T Kalathil, Abhay, Abin Simon, Praveen Basil, Kailash Dutt, Hariprasad CM,

Maya Menon, Arun Murali, Adithye Suresh, Balakrishnan Shankar and Ganesha Udupa

is with Mechanical Engineering Department, Amrita Vishwa Vidyapeetham, Kollam,

Kerala 690525 INDIA(e-mail: sreekuttan44440@gmail.com and

ammasganesh@gmail.com)

Design and Development of an Intelligent Rover for Mars

Exploration

Aswath S, Unnikrishnan VJ, Sreekuttan T Kalathil, Abin Simon, Hariprasad CM, Deepu P Mathew,

Maya Menon, Praveen Basil, Ragesh Ramachandran, Abhay Sengar, Arjun Balakrishnan, Kailash

Dutt, Arun Murali, Chinmaya Krishna Tilak, Amal Suresh, Adithye Suresh, Balakrishnan Shankar and

Ganesha Udupa

"Copyright © 2015 by ASWATH. Published by The Mars Society with permission"

This is a significant improvement to the existing rocker bogie

mechanism which provides traction using its body weight

alone. Moreover this is done without compromising the

strength of the chassis. The chassis has a factor of safety of 3.2

as per Finite Elemental Analysis. The leg, which is a

combination of the four bar linkage, spring-damper and the

linear actuator, provides assistance for the rover to traverse

over small hindrances. A member is hinged to the chassis. One

end of that member is pinned to the actuator and the outer end

to a four bar linkage, making the system stable ad flexible at

the same time. Thus the rover mechanism that has been

described in this paper allows the rover to traverse all kinds of

surfaces while maintaining stability and protecting the

instruments that the rover carries.

Figure 1. SOLIDWORKS model of the rover with front spider-legs elevated

To enable the rover to function in a semi-autonomous mode a

number of sensors have been used in the system. To avoid

catastrophic damage to the rover due to widely varying

terrains, an ultra-sonic sensor is used. Much like the effect of

a reflex action in the human body, the sensor detects the

anomaly and sends the data to the microcontrollers for

stopping the rover and averting any danger.

The mechanical system that controls the rover’s motor system

is quite complex but extremely efficient. The array of sensors

combined with system containing a number of commonly

available microcontrollers and microprocessors, makes the

movement and the working of the rover extremely accurate

and comfortably feasible. The motor drivers and the sensors

used are interfaced with microcontrollers like the Arduino and

is further controlled using state of the art microprocessors like

Raspberry pi. The Rover has been design with a semi-

autonomous control which allows for fast error correction as

well as efficient control. This papers describes both the overall

working as well as that of the individual subsystems present

in the rover.

II. ROVER MECHANICAL DESIGN

The design of the rover is to allow it to traverse rough and

rocky terrain which at present is not possible using

conventional vehicle design. Therefore the major aim is to

design a rover which has an effective mechanism removing

the disadvantage of modern day rovers. The chassis designed

is in accordance with the set of rules and requirements that

have to be met in order to contest in the event. There are

certain restrictions set on the length and width of the chassis,

its overall weight, ground clearance etc. by the governing

body of the “University Rover Challenge 2015” and it was

made mandatory that the rules be followed by the competing

teams.

A. Material Selection

Table 1. Material Properties of Aluminum 6061 Alloy

Performance and strength are the major parameters which reflect the reliability of a vehicle. While designing and fabrication of the rover chassis, suitable low cost material had to be selected which maintained high strength to weight ratio thereby improving the performance of the rover. Considering various parameters like yield strength, material availability, density, strength to weight ratio and mainly the availability and cost of the material, various options were explored. The search narrowed down to either graded aluminum or composite materials. Composite materials like Carbon Fiber are mainly used in the conventional NASA designs of MARS rovers. Based on the factors in the table 1 we choose our material of construction as Aluminium-6061.

Aluminum 6061, a precipitation hardening alloy majorly

comprises of Magnesium and Silicon. It was chosen for its

good physical properties and great weldability. Being one of

the most common alloys of Aluminum, it is easily available

and cheap. Pre-tempered grades such as 6061-O (annealed)

and tempered grades such as 6061-T6 (solutionized and

artificially aged) and 6061-T651 (solutionized, stress-relieved

stretched and artificially aged) are the commonly available

types.

B. Chassis Model

Table 2. Channel Specifications

Property Value Ultimate strength 310 MPa

Density 0.0975 lb/in^3 Strength to weight ratio

Moderate

Machinability Highly machinable /weldable using TIG

Cost Moderate Availability Available in Indian market

Material Specification Al-6061 T6 Type of channel used Rectangular

channel Channel size 2.5 in * .5 in

Thickness 3 mm Chassis Dimensions 105cm * 80 cm

Weight 4.1 kg

"Copyright © 2015 by ASWATH. Published by The Mars Society with permission"

Figure 2. Dimensions of the channel used

Figure 3. Final Design of the chassis

In order to design and manufacture the original chassis, continuous optimization had to be done. The FOS has to be higher and the deflection should be minimal. Hence, the careful selection of the channel type is required for further modelling. For minimal deflection and increased FOS, a rectangular channel of 3mm thickness was selected as the suitable channel. The rectangular channel of 3mm thickness is capable of withstanding both vertical and longitudinal load. The figure 2 shows the channel dimension and the table 2 shows channel specification. As most of the loads are exerted upon the mounting regions of linear actuators, the channel can now take fluctuating loads. The final design incorporates enough space which satisfies the component restraints and provides necessary strength for the rover. The chassis analysis was done after designing the final chassis. The figure 3 shows the final chassis design.

III. STATIC ANALYSIS OF MODEL

For the static analysis, the fixed supports were given as the

support members of C arms. A force of 500N is given to each

of the leg members. The figure 4 shows the distribution of

forces and the fixed support whereas the figure 5 shows the

meshing. The figure 6 and figure 7 shows the safety of factor

and total deformation.

Figure 4 Distribution of forces and the fixed supports

Figure 5. Meshing

Figure 6. Factor of Safety

Figure 7. Total Deformation

The values obtained from the FEA analysis are: Factor of

safety=5.8571(WithstandHighLoad),Deformation=0.001886c

m (Little Deformation) and Max Equivalent Stress=

4.263*107 Pa(Low Stress). Analyzing the data it can be

concluded that the chassis is strong and can easily withstand

"Copyright © 2015 by ASWATH. Published by The Mars Society with permission"

high strength. Therefore the chassis need not be further

optimized. The chassis is then built with real time boundary

conditions. The figure 8 shows the real chassis model.

Figure 8. Real time chassis model

IV. MECHANICS DEVELOPMENT AND KINEMATIC ANALYSIS

For the chassis that has been built, a proper mechanism has to

be developed which enables the legs of a vehicle to traverse

up steps/rocks and still be able take the impacts of varying

ground terrain. The primary motive of the mechanism is to

allow the rover to a climb high stepped terrain and still have a

suspension system in place to provide restoring force for the

legs to come down and provide traction for the wheels over

the ground terrain. Such a mechanism will allow rovers to

travel rough and rocky terrain while at present is not possible

for conventional rovers.

In currently used designs, there is a limit to the height that the

rover can traverse and it is extremely difficult for these

designs to climb up very high steps. Using suspension designs

with very soft shocks can cover rough and rocky terrain to an

extent but unfortunately it is impossible for it to climb up huge

steps and rocks. It is well known that an unexplored terrain

can have unexpected challenges. Thus it is essential for a

mechanism to exist which can overcome such unexpected

challenges. It is possible to test the conventional designs in

unexplored areas, but these designs tend to suffer from

disadvantages which would prevent them from prolonged use

hence such designs are not feasible. Thus there is a need for a

novel and innovative design which will enable rovers to face

unaccounted landscape challenges and allow it to carry on

with the unmanned exploration, without human intervention

or repair issues.

A. The Spider Mechanism

The spider-leg mechanism ensures that the vehicle can traverse over a heights far greater than the chassis height. This could extend as far as thrice the diameter of the wheels. Additionally, since the mechanism is actuator-powered, the slope of the rover can be adjusted in such a way that it does not topple for a wide range of inclination and allows the rover to traverse over highly rugged or uneven terrain. It provides a large amount of traction with the ground even in terrains where there is a negative slope or vertical drop of around 1m using a spring-damper suspension mechanism and it achieves this without compromising on the strength of the chassis.

B. Line Diagram Depiction Showing Initial Position

Figure 9. Wheel in ground level

Fig 9 and 10 depicts how the spider legs help to support the

load when all the wheels are in ground. Notice that initially,

all the linkages are pivoted at the center point of Sl no 3 in

Figure 9. This pivot point moves only when the rover

encounters an unexpected terrain. The springs are mainly

involved in traction control and in supporting the weight.

Figure 10. The complete side view of the spider legs

Figure 10 clearly depicts that the spider-leg, which is a

combination of the four bar linkage, spring-damper and the linear actuator, provides assistance for the rover to traverse over small hindrances. As mentioned earlier, one link of the mechanism is hinged to the chassis. One end is pinned to the actuator and the other end to a four bar linkage.

C. Line Diagram Depictions Showing the Movements of the

Rover

Figure 11. An example spider-leg mechanism approaching a stepped terrain

In figure 11, an example of the working of the spider-leg

mechanism is shown at its mean position. At this position the

links are able to transmit the shocks of varying terrain to the

shock absorber. When the wheels of the spider-leg mechanism

encounter a small obstacle relative to its wheel size it is able

"Copyright © 2015 by ASWATH. Published by The Mars Society with permission"

to easily overcome the obstacle as the shock absorber mounted

on the top of the wheel’s link gets compressed and the lift of

the wheel is compensated this way.

Figure 12. An example spider-leg mechanism raising itself.

In figure 12, as the spider-leg mechanism encounters a high

obstacle the linear actuator is retracted wirelessly and this

causes the link mechanism to extend out and reach a greater

height, the shock on top of the mechanism is also compressed.

However to get maximum reach and traction there needs to be

2 spider legs in front of the vehicle. Therefore 2 legs are raised.

After this initial step, the vehicle rests on the middle 4 wheels

and the 2 rear spider legs. The lifting of the front spider-legs

allows the vehicle to reach terrain previously inaccessible and

gain traction on top of the high terrain.

Figure 13. An example spider-leg mechanism overcoming a stepped terrain

In Figure 13, to effectively climb over a high obstacle a total

of 4 spider-legs are required on a vehicle with individual

drives, 2 spider legs at the front, which can be raised onto the

high terrain and gain traction on the terrain and 2 spider legs

at the rear of the vehicle. The legs at the rear lower onto the

ground effectively lifting the vehicle and giving a push to the

entire vehicle while the spider legs in front of the vehicle act

to gain traction at the top of the obstacle and effectively pulls

the entire vehicle up. This combination of the two forces allow

the vehicle to overcome high stepped terrain.

C. Software Design Depiction

Figure 14.1 Solid works rendered image of the mechanism

A Solid works model was designed and the rover assembly

was completed. This was essential for the manufacturing of

the model. The figure 14.1 shows the solid works rendered

image of the mechanism and figure 14.2 shows the isometric

view of the entire rover making it easier to study the

mechanism.

Figure 14.2 An isometric view of the overall rover

V. KINEMATIC ANALYSIS OF THE MECHANISM

Kinematic analysis is an integral part of the mechanism

implementation. It helps us to study the trajectory of points,

bodies (objects) and systems of bodies without considering

the motion.

A. Formulation of Velocity Polygon

If a number of bodies are assembled in such a way that the

motion of one causes a constrained and predictable motion to

others, it is known as a mechanism. The function of a

mechanism is to transmit and modify the associated motion.

The leg of the rover moves according to motion which

constitutes a planar mechanism. For planer mechanism the

degree of freedom of the mechanism can be calculated by

Grueblers Criterion.

F=3(N-1)-2j

Where j= (1/2) (2N2+3N3)

Where,

N= the total number of joints, N2= the number of binary joints,

N3= the number of ternary joints

According to the Grubeler's criterion if for a planar linkage the

degree of freedom is one, then it is called a mechanism.

"Copyright © 2015 by ASWATH. Published by The Mars Society with permission"

A spring in a mechanism can be converted to a turning pair.

This is because the action of a spring is to elongate or shorten

as it gets subjected to in tension or compression. A similar

variation is obtained by two binary link joined by a turning

pair.

Figure 15 Mechanism Link Diagram

The validation of the mechanism is done as shown below.

The mechanism consists of four binary links and two ternary

links as shown in the figure 15.

Hence the total number of links are six.

F = 3(N-1) -2 J;

2J = 2* 𝑛2 + 3*𝑛3

=2*4 +3*2 =14

F = 3(6-1) - 14

=1

Hence it is a mechanism.

The links move dependent of each other. Hence the velocities

of each link maintain a relation. So once we experimentally

find a velocity of a link, we can find out the absolute velocity

as well as the relative velocity of other links with respect to

reference links. To find out velocities this way, we must

follow certain laws and constraints. They include laws like,

the velocities of a joint are perpendicular to the direction of

motion of a link and that the meeting points of line of action

of velocity lines gives the velocity of the links with respect to

ground.

Applying this method on the leg mechanism of the rover, the

initial velocity given was found to be 7 cm/sec. This velocity

was given at the wheel of the rover. An assumption was made

that the velocity of the wheel will be the same as that of the

legs of the rover while traversing the terrain. From the velocity

polygon it was understood that the velocity with which the

spring displaces is about one tenth of the velocity with which

the wheel moves up. Figure 16.1 and 16.2 shows velocity

diagram of links 5, 7 and 6, 7.

Figure 16.1 Velocity diagram of links 5, 7

Initially we assume the velocity of joint 7 to be 7

cm/sec. Later we have to find out the angular velocity

of link 57 by the relation V = r ω.

W57 =V7 /L57

W57 =11.909/19.3=0.617 rad/sec

Figure 16.2. Velocity Diagram links 6,7

The known velocities are V7 and the line of action of V6 and

line of action of V6, 7

V6 = 0.8 cm/sec and V6,7=11.5cm/sec

W6 =W6,7 =(V6,7 / L6,7)=(11.5/7)=1.15 rad/sec

W3=V6/L4,6 =(0.8/20)=0.04 rad/sec

V3=W3*L3,4=0.04*10=0.4cm/sec

Now from the known v3 we find out v2.

V2=5.7cm/sec and V3,2=6.3cm/sec

Figure 16.3. Velocity Polygon Diagram

Finally velocity polygon is drawn showing all the absolute

velocities and relative velocities of each link with respect to

other links as shown in figure 16.3.

VI. DYNAMIC ANALYSIS USING ADAMS

The various parameters for the newly developed mechanism

is found out with the help of ADAMS software. The

parameters that were to be found out include velocity of every

joints and links, acceleration of the links and joints ,angular

velocity, angular acceleration ,force and torque acting on

various parts and finally the deformations of the spring,

deformation velocity and the forces that act on the spring.

These are important for validating the new design. The basic

governing equations that govern the kinematic analysis in

ADAMS are based on the Eulerian and Lagrangian dynamics.

"Copyright © 2015 by ASWATH. Published by The Mars Society with permission"

The mechanism of the leg of our rover was analyzed in

ADAMS and for the acceleration due to gravity 9.81, with the

weight of the members the graphs were plotted for each link.

The results for each part that was analyzed are given below.

A. Simulation of the Spider Leg Using ADAMS

Figure 17. Simulation in ADAMS

The leg mechanism was kinematically analyzed in ADAMS

software as shown in figure 17 by giving the center of gravity

for each specific links and specifically giving the connectors

to each link. Afterwards motions were assigned to each of the

joints. Later graphs were plotted when simulated. Some of

these are as shown below from18.1 to 18.5.

Figure 18.1. Length vs time graph of rectangular link 1

Figure 18.2. Angle Vs Time graph for wheel

Figure 18.3.Acceleration Vs time graph for wheel

Figure 18.4 Deformation Vs time graph for spring

Figure 18.5Force Vs time graph for spring

VII. LINKAGE SPRING DESIGN

The linkage spring has to be carefully designed to support the

weight while traversing a terrain in order in turn providing

traction. For this, various parameters like spring rate (spring

constant), spring material, free length etc. has to be

considered, and number of coils etc. had to be fixed.

The cycle shock was the best available alternative for the

shock absorption and maintaining traction. But the standard

available cycle shocks have a very high stiffness rate. A spring

has to be custom made for the specific purpose. So in order to

do that, a spring had to be selected whose free length and the

compressed length are known. The figure 19 shows the

dimension of the spring used. But it is to be evaluated whether

"Copyright © 2015 by ASWATH. Published by The Mars Society with permission"

the spring can support prescribed weight. The load calculation

for the spring is as follows.

Figure 19 Spring Dimensions

To calculate the spring rate we know that,

Wire diameter = 4 mm

Free length = 118 mm

Compressed length = 80

No of active coils = 13

Outer diameter = 36 mm

Deflection = Free length – Compressed length

= 118 – 80 = 38 mm

Spring Rate =Spring Rate/ Stiffness = (Modulus of spring

steel * (wire diameter) 4)/ (8*No of active coils*(mean coil

diameter) 3

Spring Rate= ((209*109)*(4*10-3)4)/ (8*13*(36*10-3)3

=5957N/m

Force which can compress 1” = spring rate * deflection

= 5957 Nm * (38 * 10-3)

= 226 N

Hence the load will be approx. 23kgf required for the spring

to compress 1” which is the desired value.

VIII. WEIGHT DISTRIBUTION

The weight distribution is the apportioning of weight within a

vehicle. Typically it is written in the form x: y where x is the

percentage in front and y is the percentage in the back. In a

vehicle which relies on gravity in some way, weight

distribution directly affects a variety of the vehicle

characteristics including handling, acceleration and traction.

For this reason weight distribution varies with vehicle’s

intended usage. The following section shows how the weight

is distributed when the Mars Rover is in different position.

A. The Rover is in Normal Position

The figure 20.1 shows the rover in normal position with

X=78cm, Y=396cm and Z=714cm.

Figure 20.1 Normal Position

The calculation of weight distribution is as follows

Overall length = 230 cm

When four wheels are in ground the weight distribution is

50: 50, i.e. the center of gravity lies in the center as in Figure

20.1. The vehicle is stable as the CG lies in the center of the

rover.

B. The Rover’s One Leg is in the Lifted Position

The figure 20.2 shows the rover in one leg lifted position with

X=78cm, Y=400cm and Z=711cm

Figure 20.2 Rover’s One Leg Lifted Position

The calculation of weight distribution is as follows

Shift in length = 4 cm

Ratio = 230/ (115 + 4) = 1.932

Overall Weight Distribution = 25 * 1.932=48.3

Hence the weight distribution is 51.7: 48.3

C. The Rover’s Both Legs are Lifted

The figure 20.3 shows the rover in both legs lifted position

with X=78cm, Y=401cm and Z=711cm

Figure 20.3 Rover’s Both the Legs are Lifted

The calculation of weight distribution is as follows

Shift in length = 5 cm

Ratio = 230/ (115 + 5) = 1.9166

Overall Weight Distribution = 25 * 1.9166 = 47.915

Hence the weight distribution is 52.1: 47.9

The weight distribution was well optimized when compared to

previous versions. In the final model there is a significant

difference in the weight distribution and in the CG value. After

optimization, the CG shift is very low which makes the rover

stable with the proper working of the mechanism. The figure

21 shows below shows the final prototype of the Mars Rover.

"Copyright © 2015 by ASWATH. Published by The Mars Society with permission"

Figure 21. Final Prototype

IX. ROBOTIC ARM This 3-linked robotic arm is an 8 degree of freedom inverse

kinematic machine. Because of its rotational capability, the 3

degree of freedom base has maximum reachability around the

rover, irrespective of the rover orientation. The arm is

equipped with a gripper turret with 3 types of end effectors.

One of them is a two link gripper mechanism. The second is a

four link gripper mechanism for circular gripping and opening

valves. The third end effector is an Archimedes screw that can

be used for soil collection. The arm body as a whole has 2

additional degrees of freedom for linear movement across the

rover body along a 100cm platform on a belt driven linear

actuator. In addition, the linear actuator and arm can rotate on

a DC stepper motor, fixed at the rover base to rotate the arm

by 360 degrees on a horizontal platform. Figure 22 shows

robotic arm and various end effectors used. This makes

equipment servicing, sample collection and astronaut assistant

tasks easier. Figure 22: Robotic arm and different end effectors available on gripper turret

X. ROVER ELECTRONICS

Figure 23: Block diagram of electronic system of the rover

The Figure 23 shows the electronics design block diagram of

the main rover components. The electronic system includes

the power system, sensors, camera, video transmission and

reception, robotic arm system, navigation, driver system and

radio frequency communication systems.

A. POWER SYSTEM

1. Battery: We use 16Ah 22.2V Lithium Polymer

battery, as lithium polymer provides a light weight,

reliable, reasonable current capacity, and form factor

that is good for confined space. 2. Battery Monitoring System: We use battery

monitoring circuits and low voltage alarm.

B. DRIVE SYSTEM

1. Motors: We use 18V brushed DC planetary gear

motors, with gearing ratio 1:256 and 76 RPM, with

Stall Torque of 300.8 kg-cm.

2. Steering Actuators: Our Rover Design uses high torque 30 RPM brushed DC gear motors as steering actuators, with shaft encoders, for making it faster and reliable actuators.

3. Motor Driver: We use a 120A motor driver, suitable

for high powered robots. The driver allows us to

control the motors with: analog voltage, radio

controls, serial and packetized serial. Overcurrent

and thermal protection are included in driver itself.

C. VIDEO SYSTEM

We use three cameras: pan/tilt camera, a camera along

with robotic arm and a Stereo vision camera (for depth

analysis and 3-dimensional view of the area)

1. Main Camera: We use a pan and tilt Night Vision CCTV

wireless camera with 1 km range.

2. Arm Camera: We use a camera with 5.8 GHz AV receiver.

This camera provides a decent vantage point of the arm end

effectors and the arm objective. This allows for precision in

"Copyright © 2015 by ASWATH. Published by The Mars Society with permission"

locating and orienting the end effector to perform various

equipment servicing tasks such as opening valves, operating

switches, etc.

D. MAIN CONTROL SYSTEM

We use INTEL-NUC processor and microcontrollers for

controlling each subsystem. Image processing is done by

Intel NUC. Other subsystems are controlled by Arduino

Mega microcontrollers.

E. COMMUNICATION SYSTEM

1. Control Radio: We use 2.4 GHz Radio Frequency 9-

channel Transmitter to control the rover. We use 2.4GHz

XBee XBP24-AWI-001, for controlling the robotic arm.

2. Video Transmission: Main camera is a wireless camera

with 2W transmission power and operating frequency of

2414-2468 MHz. The camera on the robotic arm has a

transmitter frequency of 5645-5945MHz with 500mW

power output.

3. At Base Station: We have 2.4GHz 9 channel transmitter,

5.8GHz 32 channel AV Receiver and 2.4 GHz AV

receiver, 2.4 GHz XBee Transceiver to receive sensor data

and send control signals.

F. NAVIGATION SYSTEM

Connected to an external antenna on the rover main control

board, the Garmin GPS-15x receiver (with WAAS capability)

is used to navigate and localize itself. This module provides

functionality of abstracted navigation and is connected

directly to the microcontroller, for parsing the NMEA

navigation strings.

G. SENSORS

We use the below mentioned sensors for analyzing the following

conditions:

1. Moisture Sensor: For identifying the water content in the

soil sample, we use a soil moisture meter

2. Temperature, pressure and humidity Sensor

3. PH Sensor: To determine the PH of the soil sample using

four buffer solutions

4. Distance Measurement

5. Air Quality Sensor: To determine the contents and quality

of air at a location

6. Light Sensor: For determining the light intensity at the

given location

7. Inertial Measurement Unit

8. Digital Compass: To increase the accuracy of localization

and terrain traversing

XI. ADDITIONAL FEATURES

A. STEREO VISION AUTONOMOUS NAVIGATION

SYSTEM

The rover is equipped with autonomous navigation unit that can help

in reaching required destinations without the help of manual

instructions. The heart of the system is Intel NUC Celeron processor,

and main input sensors are stereo vision cameras and ultrasonic

transducers. Stereo vision is based on Simultaneous Localization and

Mapping (SLAM) algorithm to perform intelligent navigation. The

SLAM unit takes the GPS coordinates of the destination as input and

plans the shortest path from the current location. As it traverses along

the planned path, the rover will generate the three-dimensional map

of the environment and localize itself in the developed map.

B. SWARM ROBOTS

Swarm robots, using GPS and RF communication, are used for

distributed sensing task. In order to investigate narrow, deep and

risky areas, we use two four-wheeled swarm robots (ground vehicles)

with stereo vision, which are kept in the main rover and can be

deployed when required.

C. UNMANNED AERIAL VEHICLE

UAV based stereo vision system is used to determine the ground

depth and perform obstacle mapping, and path planning. The drone

has a payload capacity of 5kg.

XII. CONCLUSION

The mars rover has been designed with an improved

mechanism when compared to existing versions and the final

prototype has been built. The rover was built with aluminum 6061

and using various mechanical techniques like water jet cutting,

TIG welding, drilling etc. The team’s design had cleared the

Critical Design Review of the University Rover Challenge 2015

conducted by Mars Society, USA. An innovative spider-leg

mechanism has been implemented in which suitable kinematic

linkage analysis and dynamic analysis were conducted to analyze

and verify whether it is capable of traversing all terrains. The

prototype manufacturing helped us to experimentally test the

mechanism, so that we could bring necessary changes to the

design. The present mechanism enables the vehicle to traverse up

steps/rocks while still being able to take the impacts of varying

terrain. In currently used designs, the height which the wheels of

a vehicle can traverse, is limited and it is extremely difficult for

these vehicles to climb up high steps. However a suspension

mechanism with very soft shocks can cover rough and rocky

terrain to an extent. Unfortunately it is impossible for them to

climb up huge steps and rocks. Study and analysis has been done

on the design and finally an optimized design in obtained. The

final design is again tested experimentally using a fully functional

prototype.

ACKNOWLEDGMENT

The authors would like to thank Mechatronics and Intelligence

Systems Research Lab, Department of Mechanical Engineering,

Amrita University, Amritapuri campus for providing support to

carry out the research and experiments.

"Copyright © 2015 by ASWATH. Published by The Mars Society with permission"

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